This hands-on look at Firefox 3.1 beta 2 shows that TraceMonkey has gotten even faster, and explores the Private Browsing feature a bit more in-depth.

The much-anticipated Firefox 3.1 beta 2 is out and about for Windows and Mac users, incorporating the faster JavaScript engine TraceMonkey as the default setting and introducing Private Browsing, which has been in development for years. There are other improvements, of course, but the big one is the ability to turn off the cache and other private data settings with a single click.

Firefox 3.1 beta 2 is the first chance the public has had to use Mozilla's long-awaited privacy feature.
(Credit: CNET Networks)

Private Browsing works similarly to Google Chrome's Incognito, or Safari's setting of the same name. Go into Tools on the Menubar and click Private Browsing, and all your movements on the Internet will not be recorded. Firefox's version of the feature saves all your tabs and closes the browsing session, re-opening a new and empty browser window. Unlike Chrome, Firefox doesn't sport a clever little icon indicating that you're browsing on the sly. The program title bar does state that you're using Private Browsing, but there's no blatant icon.

Firefox has also posted the about:config setting needed to set Private Browsing as your default browsing configuration. Once you're in the about:config, type in browser.privatebrowsing.autostart and double-click on the False setting. This will change it to True, and when you restart your browser you will automatically be in Private Browsing mode.

What's interesting about this is that it removes the indicator from the Title Bar and grays out the Private setting in the Tools menu. The only way to resume normal browsing is to change the about:config back to its original False setting. Doing this restores your last previous non-Private browsing session, tabs and all.

There is more in Firefox 3.1 beta 2 than just the ability to surf surreptitiously. TraceMonkey, the new JavaScript engine that Mozilla introduced in the previous Firefox beta, is now on by default. It feels even faster than it did in the first beta. The SunSpider JavaScript test showed 2449.2 for FF3.1 beta 2, about an 8 percent improvement over FF3.1 beta 1, with a margin of error at around 5 percent. Part of the change could be due to changes in the Gecko layout engine such as "speculative parsing" that Mozilla claims resulted in faster content rendering.

One of the big disappointments is that the new tab-switching behavior has been removed. As a serial tab abuser, I thought it was extremely useful that FF3.1 would have a visual representation of the tabs I was jumping between. Hopefully, this feature will be at least rolled out as an add-on, but I've been known to abuse those, too.

For developers, this beta includes support for Web worker threads, which I was also somewhat disappointed to learn was not a Mozilla-sponsored fashion plan for style-deficient techies. Instead, they're about the JavaScript implementation and what kind of requests can be made in the code.

Firefox 3.1 beta 2 will not be the final tester update. According to Mozilla, it will be followed by at least one more beta release.